This Phase 4, multicenter, randomized, double-blind, active-controlled, non-inferiority study aims to evaluate the non-inferiority of Stoem Tab. compared to Stillen Tab. (Dong-A ST Co., Ltd.) in patients with acute or chronic gastritis. Participants will receive either Stoem Tab. or Stillen Tab. for 2 weeks. The primary outcome is the effective rate of gastric mucosal erosion at Week 2, assessed by upper gastrointestinal endoscopy and evaluated by an independent reviewer, defined as the proportion of participants achieving at least a 50% improvement in erosion score compared to baseline.